Debunking the myth of the sand-burrowing
minnow

It's a popular refrain here in
central New Mexico come summer: The silvery minnow can hunker down,
bury itself in a dry streambed and outlast drought.

Whenever the river slows and its bed begins to dry, I'm inevitably
informed that the Rio Grande has always dried, and the four-inch
long minnow has always survived. This year, I received a letter
pointing out that "old-timers" and "local observers" know that
minnows can bury themselves and their eggs in the sandy river
bottom. I was also told that "desert fish have evolved to deal with
drought."

I've seen the bumper sticker that says "A woman
without a man is like a fish without a bicycle." But in my mind, a
fish without water is just a dead fish, one that's likely to be
eaten by a bird or maybe even run over by a bicycle. Not being an
ichthyologist, however, I decided to consult with biologists,
geneticists and fisheries scientists and ask whether the minnow can
live in sand to swim another day.

"BS," began a message
that came to my inbox within the hour. This fisheries biologist,
who had certainly been asked the question more than once, wrote
that when the Middle Rio Grande dried in 1996, the manager of
Bosque del Apache refuge took a backhoe to the dry riverbed. He,
along with a handful of farmers invited to watch, dug six feet into
the riverbed — and nary an egg was found.

"Fish
don't live in sand — dry or wet," the testy biologist
continued in his e-mail.

Fish do burrow in sand to
survive drought in Africa and Australia. Known as
aestivating fish, they include the lungfish and
salamander fish. But aestivating fish, one
geneticist assured me, do not live in North America.

The
minnow used to swim throughout much of the 1,850 mile-long Rio
Grande; in fact, it was once the most populous fish species in the
Middle Rio Grande. It also lived in the Pecos River, which flows
through eastern New Mexico. The fish is now found in small numbers
in a 157-mile stretch of the Rio Grande, and it is completely gone
from the Pecos, which nowadays also dries each summer.

Another biologist told me that most of the fish species that occupy
the Rio Grande are closely related to Mississippi River-drainage
fish and are not really desert-adapted. He added that "these fish
occupy medium-to-large perennially flowing rivers that flow through
arid areas." This bears repeating: The fish live in rivers that
flow through dry areas.

Not only that, but even if
sections of the Rio Grande dried up in the past, they never dried
completely. When one portion of the riverbed dried, water likely
remained in an adjacent bend or oxbow. Without dams to stop them,
minnow eggs and larvae from upstream waterways would have drifted
downstream, re-colonizing the reaches that had suffered drying.

Today's Rio Grande does not bend and meander throughout
the valley; it is carefully managed to flow within a relatively
narrow channel for short stretches between diversions and dams.
Now, there are 16 major dams and diversions on the Rio Grande
between its headwaters in Colorado and the Gulf of Mexico. When one
portion of the river dries, the fish can't simply swim up or
downstream. When, say, 80 miles of the river dries, as it did in
2003, biologists must salvage what fish they can, pack them in
plastic bags with water, then truck them to a wet portion of the
river. Then, from the fall through the spring, when flows are
higher, it's up to biologists to stock the river from fish they've
raised in tanks.

A second geneticist pointed out that we
didn't collect much historical flow data before dams and
diversions.

"That timescale (from when water managers
started recording flows) is pretty negligible when it comes to
evolution," she said, "even for a minnow with a short generation
time." In other words, even the short-lived minnow can't evolve
fast enough to be able to live without water. That's like expecting
humans to evolve within a few hundred years to survive while
breathing carbon monoxide.

It's critical that journalists
report many sides of any story. But let's lay to rest the myth of
the amazingly resilient silvery minnow. There's absolutely no proof
that it burrows into the sand and hangs on in the dry streambeds of
the river, and as far as I can tell, there's little proof that the
"old-timers" who tell such tales exist either.

Laura Paskus is a contributor to Writers on the Range, a
service of High Country News (hcn.org). She is
the paper's Southwest editor in Albuquerque, New
Mexico.